Streams, Shells, and Substructures in the Accretion-Built Stellar Halo of NGC 300

TL;DR

Deep optical observations of NGC 300's stellar halo reveal multiple streams and shells indicative of past accretion events, including a large low surface brightness stream and a distant globular cluster, highlighting accretion's role in dwarf galaxy halo formation.

Contribution

First detailed detection of multiple stellar streams and shells in NGC 300's halo, providing evidence for accretion-driven assembly in a Magellanic Cloud analog.

Findings

Discovery of a large, low surface brightness stellar stream extending over 40 kpc.

Identification of a distant, metal-poor globular cluster in NGC 300's halo.

Evidence supporting accretion as a key process in dwarf galaxy halo formation.

Abstract

We present deep optical observations of the stellar halo of NGC 300, an LMC-mass galaxy, acquired with the DEEP sub-component of the DECam Local Volume Exploration survey (DELVE) using the 4 m Blanco Telescope. Our resolved star analysis reveals a large, low surface brightness stellar stream ($M_{V}\sim-8.5$; [Fe/H] $= -1.4\pm0.15$) extending more than 40 kpc north from the galaxy's center. We also find other halo structures, including potentially an additional stream wrap to the south, which may be associated with the main stream. The morphology and derived low metallicities of the streams and shells discovered surrounding NGC 300 are highly suggestive of a past accretion event. Assuming a single progenitor, the accreted system is approximately Fornax-like in luminosity, with an inferred mass ratio to NGC 300 of approximately $1:15$. We also present the discovery of a metal-poor globular cluster ($R_{\rm{proj}}=23.3$~kpc; $M_{V}=-8.99\pm0.16$; [Fe/H] $\approx-1.6\pm0.6$) in the halo of NGC 300, the furthest identified globular cluster associated with NGC 300. The stellar structures around NGC 300 represent the richest features observed in a Magellanic Cloud analog to date, strongly supporting the idea that accretion and subsequent disruption is an important mechanism in the assembly of dwarf galaxy stellar halos.